[skip ci] Update version

* Bugfix/odr violations (#47)

* Make common non-member functions inline, remove unreachable line from get_line_buffer

* [skip ci] Fix namespace comments

* Resolve clang-tidy warnings (#48)

* Resolve clang-tidy warnings, update single_header_generator.py

* Update single header test, resolve additional clang-tidy warnings

* Add header and raw_header methods,  update header usage methods error handling, write new and update existing unit tests

* Update parser error messages, fix parser tests

* Add [[nodiscard]] where fitting, update unit tests (#49)

* Add const where fitting, make splitter class members private, add #pragma once to ssp.hpp

* Modify header parsing for empty headers, update old and add new tests for header parsing

* Enable the parser to accept a header with one empty field, update unit tests

* Fix test CMakeLists.txt typo

CMakeLists.txt

@@ -2,7 +2,7 @@ cmake_minimum_required(VERSION 3.14)
 
 project(
     ssp
-    VERSION 1.7.2
+    VERSION 1.8.0
     DESCRIPTION "csv parser"
     HOMEPAGE_URL "https://github.com/red0124/ssp"
     LANGUAGES CXX

README.md

@@ -74,7 +74,7 @@ Bill (Heath) Gates 65 3.3
 
 # Single header
 
-The library can be used with a single header file **`ssp.hpp`**, but it suffers a slight performance loss when converting floating point values since the **`fast_float`** library is not present within the file.
+The library can be used with a single header file **`ssp.hpp`**, but it suffers a significant performance loss when converting floating point values since the **`fast_float`** library is not present within the file.
 
 # Installation
 
@@ -92,7 +92,7 @@ The library supports [CMake](#Cmake) and [meson](#Meson) build systems
 
 ## Headers
 
-The parser can be told to use only certain columns by parsing the header. This can be done by using the **`use_fields`** method. It accepts any number of string-like arguments or even an **`std::vector<std::string>`** with the field names. If any of the fields are not found within the header or if any fields are defined multiple times it will result in an error.
+The parser can be told to use only certain columns by parsing the header. This can be done with the **`use_fields`** method. It accepts any number of string-like arguments or even an **`std::vector<std::string>`** with the field names. If any of the fields are not found within the header or if any fields are defined multiple times it will result in an error.
 ```shell
 $ cat students_with_header.csv
 Id,Age,Grade
@@ -116,7 +116,7 @@ James Bailey 2.5
 Brian S. Wolfe 1.9
 Bill (Heath) Gates 3.3
 ```
-The header can be ignored using the **`ss::ignore_header`** [setup](#Setup) option or by calling the **`ignore_next`** method after the parser has been constructed.
+The header can be ignored using the **`ss::ignore_header`** [setup](#Setup) option or by calling the **`ignore_next`** method after the parser has been constructed. If the header has been ignored calling any method related to header usage will result in a compilation error.
 ```cpp
 ss::parser<ss::ignore_header> p{file_name};
 ```
@@ -124,10 +124,10 @@ The fields with which the parser works with can be modified at any given time. T
 ```cpp
     // ...
     ss::parser<ss::throw_on_error> p{"students_with_header.csv"};
-    p.use_fields("Id", "Grade");
+    p.use_fields("Grade");
 
-    const auto& [id, grade] = p.get_next<std::string, float>();
-    std::cout << id << ' ' << grade << std::endl;
+    const auto& grade = p.get_next<std::string>();
+    std::cout << grade << std::endl;
 
     if (p.field_exists("Id")) {
         p.use_fields("Grade", "Id");
@@ -139,10 +139,32 @@ The fields with which the parser works with can be modified at any given time. T
 ```
 ```shell
 $ ./a.out
-James Bailey 2.5
-40 Brian S. Wolfe
-65 Bill (Heath) Gates
+2.5
+1.9 Brian S. Wolfe
+3.3 Bill (Heath) Gates
 ```
+The header is parsed with the same rules as other rows, the only difference is that **`multiline`** will be disabled when parsing the header. To get the data that is
+present in the header as a **`std::vector<std::string>`**, the **`header`** method can be used, and to get the header line before it has been parsed, the **`raw_header`** method can be used:
+```cpp
+    // ...
+    ss::parser<ss::throw_on_error> p{"students_with_header.csv"};
+
+    std::cout << p.raw_header() << std::endl;
+
+    for (const auto& field: p.header()) {
+        std::cout << "> " << field << std::endl;
+    }
+    // ...
+```
+```shell
+$ ./a.out
+Id,Age,Grade
+> Id
+> Age
+> Grade
+```
+Methods related to headers can also fail, the error handling of these is done in the same way as for other methods.
+
 ## Conversions
 An alternate loop to the example above would look like: 
 ```cpp

include/ss/parser.hpp

@@ -531,10 +531,6 @@ private:
 
     [[nodiscard]] bool strict_split(header_splitter& splitter,
                                     std::string& header) {
-        if (header.empty()) {
-            return false;
-        }
-
         if constexpr (throw_on_error) {
             try {
                 splitter.split(header.data(), reader_.delim_);
@@ -562,11 +558,6 @@ private:
 
         for (const auto& [begin, end] : splitter.get_split_data()) {
             std::string field{begin, end};
-            if (field.empty()) {
-                handle_error_duplicate_header_field(field);
-                header_.clear();
-                return;
-            }
             if (std::find(header_.begin(), header_.end(), field) !=
                 header_.end()) {
                 handle_error_duplicate_header_field(field);

meson.build

@@ -6,7 +6,7 @@ project(
       'cpp_std=c++17', 
       'buildtype=debugoptimized',
       'wrap_mode=forcefallback'],
-  version: '1.7.2',
+  version: '1.8.0',
   meson_version:'>=0.54.0')
 
 fast_float_dep = dependency('fast_float')

ssp.hpp

@@ -2805,10 +2805,6 @@ private:
 
     [[nodiscard]] bool strict_split(header_splitter& splitter,
                                     std::string& header) {
-        if (header.empty()) {
-            return false;
-        }
-
         if constexpr (throw_on_error) {
             try {
                 splitter.split(header.data(), reader_.delim_);
@@ -2836,11 +2832,6 @@ private:
 
         for (const auto& [begin, end] : splitter.get_split_data()) {
             std::string field{begin, end};
-            if (field.empty()) {
-                handle_error_duplicate_header_field(field);
-                header_.clear();
-                return;
-            }
             if (std::find(header_.begin(), header_.end(), field) !=
                 header_.end()) {
                 handle_error_duplicate_header_field(field);

test/CMakeLists.txt

@@ -33,10 +33,11 @@ set(DOCTEST "${FETCHCONTENT_BASE_DIR}/doctest-src")
 enable_testing()
 
 foreach(name IN ITEMS test_splitter test_parser1_1 test_parser1_2
-                      test_parser1_3 test_parser1_4 test_converter
-                      test_extractions test_parser2_1 test_parser2_2
-                      test_parser2_3 test_parser2_4 test_parser2_5
-                      test_parser2_6 test_extractions_without_fast_float)
+                      test_parser1_3 test_parser1_4 test_parser1_5
+                      test_converter test_extractions test_parser2_1
+                      test_parser2_2 test_parser2_3 test_parser2_4
+                      test_parser2_5 test_parser2_6
+                      test_extractions_without_fast_float)
     add_executable("${name}" "${name}.cpp")
     target_link_libraries("${name}" PRIVATE ssp::ssp fast_float
                                             doctest::doctest)

test/meson.build

@@ -6,6 +6,7 @@ tests = [
   'parser1_2',
   'parser1_3',
   'parser1_4',
+  'parser1_5',
   'splitter',
   'converter',
   'extractions',

test/test_parser1_4.cpp

@@ -178,7 +178,8 @@ void test_invalid_fields(const std::vector<std::string>& lines,
 
     auto check_header = [&lines](auto& p) {
         if (lines.empty()) {
-            CHECK(p.header().empty());
+            CHECK_EQ(p.header().size(), 1);
+            CHECK_EQ(p.header().at(0), "");
             CHECK_EQ(merge_header(p.header(), ","), p.raw_header());
         } else {
             CHECK_EQ(lines[0], merge_header(p.header()));
@@ -263,7 +264,7 @@ void test_invalid_fields(const std::vector<std::string>& lines,
     }
 }
 
-TEST_CASE_TEMPLATE("test invalid fheader fields usage", T,
+TEST_CASE_TEMPLATE("test invalid header fields usage", T,
                    ParserOptionCombinations) {
     test_invalid_fields<T>({}, {});
 
@@ -397,178 +398,3 @@ TEST_CASE_TEMPLATE("test invalid rows with header", T,
         CHECK_EQ(merge_header(p.header()), p.raw_header());
     }
 }
-
-TEST_CASE_TEMPLATE("test invalid header", T, ParserOptionCombinations) {
-    constexpr auto buffer_mode = T::BufferMode::value;
-    using ErrorMode = typename T::ErrorMode;
-
-    unique_file_name f{"invalid_header"};
-
-    // Empty header
-    {
-        std::ofstream out{f.name};
-        out << "" << std::endl;
-        out << "1" << std::endl;
-    }
-
-    {
-        auto [p, _] = make_parser<buffer_mode, ErrorMode>(f.name);
-        CHECK(p.header().empty());
-        CHECK_EQ(merge_header(p.header()), p.raw_header());
-        CHECK(p.valid());
-    }
-
-    // Unterminated quote in header
-    {
-        std::ofstream out{f.name};
-        out << "\"Int" << std::endl;
-        out << "1" << std::endl;
-    }
-
-    {
-        auto [p, _] =
-            make_parser<buffer_mode, ErrorMode, ss::quote<'"'>>(f.name);
-        auto command = [&p = p] { std::ignore = p.header(); };
-        expect_error_on_command(p, command);
-        CHECK_EQ(p.raw_header(), "\"Int");
-    }
-
-    {
-        auto [p, _] =
-            make_parser<buffer_mode, ErrorMode, ss::quote<'"'>, ss::multiline>(
-                f.name);
-        auto command = [&p = p] { std::ignore = p.header(); };
-        expect_error_on_command(p, command);
-        CHECK_EQ(p.raw_header(), "\"Int");
-    }
-
-    {
-        auto [p, _] = make_parser<buffer_mode, ErrorMode, ss::quote<'"'>,
-                                  ss::escape<'\\'>, ss::multiline>(f.name);
-        auto command = [&p = p] { std::ignore = p.header(); };
-        expect_error_on_command(p, command);
-        CHECK_EQ(p.raw_header(), "\"Int");
-    }
-
-    // Unterminated escape in header
-    {
-        std::ofstream out{f.name};
-        out << "Int\\" << std::endl;
-        out << "1" << std::endl;
-    }
-
-    {
-        auto [p, _] =
-            make_parser<buffer_mode, ErrorMode, ss::escape<'\\'>>(f.name);
-        auto command = [&p = p] { std::ignore = p.header(); };
-        expect_error_on_command(p, command);
-        CHECK_EQ(p.raw_header(), "Int\\");
-    }
-
-    {
-        auto [p, _] = make_parser<buffer_mode, ErrorMode, ss::escape<'\\'>,
-                                  ss::multiline>(f.name);
-        auto command = [&p = p] { std::ignore = p.header(); };
-        expect_error_on_command(p, command);
-        CHECK_EQ(p.raw_header(), "Int\\");
-    }
-
-    {
-        auto [p, _] = make_parser<buffer_mode, ErrorMode, ss::escape<'\\'>,
-                                  ss::quote<'"'>, ss::multiline>(f.name);
-        auto command = [&p = p] { std::ignore = p.header(); };
-        expect_error_on_command(p, command);
-        CHECK_EQ(p.raw_header(), "Int\\");
-    }
-}
-
-template <typename T>
-void test_ignore_empty(const std::vector<X>& data) {
-    constexpr auto buffer_mode = T::BufferMode::value;
-    using ErrorMode = typename T::ErrorMode;
-
-    unique_file_name f{"ignore_empty"};
-    make_and_write(f.name, data);
-
-    std::vector<X> expected;
-    for (const auto& d : data) {
-        if (d.s != X::empty) {
-            expected.push_back(d);
-        }
-    }
-
-    {
-        auto [p, _] =
-            make_parser<buffer_mode, ErrorMode, ss::ignore_empty>(f.name, ",");
-
-        std::vector<X> i;
-        for (const auto& a : p.template iterate<X>()) {
-            i.push_back(a);
-        }
-
-        CHECK_EQ(i, expected);
-    }
-
-    {
-        auto [p, _] = make_parser<buffer_mode, ErrorMode>(f.name, ",");
-        std::vector<X> i;
-        size_t n = 0;
-        while (!p.eof()) {
-            try {
-                ++n;
-                const auto& a = p.template get_next<X>();
-                if (data.at(n - 1).s == X::empty) {
-                    CHECK_FALSE(p.valid());
-                    continue;
-                }
-                i.push_back(a);
-            } catch (...) {
-                CHECK_EQ(data.at(n - 1).s, X::empty);
-            }
-        }
-
-        CHECK_EQ(i, expected);
-    }
-}
-
-TEST_CASE_TEMPLATE("test various cases with empty lines", T,
-                   ParserOptionCombinations) {
-    test_ignore_empty<T>(
-        {{1, 2, "x"}, {3, 4, "y"}, {9, 10, "v"}, {11, 12, "w"}});
-
-    test_ignore_empty<T>(
-        {{1, 2, X::empty}, {3, 4, "y"}, {9, 10, "v"}, {11, 12, "w"}});
-
-    test_ignore_empty<T>(
-        {{1, 2, "x"}, {3, 4, "y"}, {9, 10, "v"}, {11, 12, X::empty}});
-
-    test_ignore_empty<T>(
-        {{1, 2, "x"}, {5, 6, X::empty}, {9, 10, "v"}, {11, 12, "w"}});
-
-    test_ignore_empty<T>(
-        {{1, 2, X::empty}, {5, 6, X::empty}, {9, 10, "v"}, {11, 12, "w"}});
-
-    test_ignore_empty<T>(
-        {{1, 2, X::empty}, {3, 4, "y"}, {9, 10, "v"}, {11, 12, X::empty}});
-
-    test_ignore_empty<T>(
-        {{1, 2, "x"}, {3, 4, "y"}, {9, 10, X::empty}, {11, 12, X::empty}});
-
-    test_ignore_empty<T>(
-        {{1, 2, X::empty}, {3, 4, "y"}, {9, 10, X::empty}, {11, 12, X::empty}});
-
-    test_ignore_empty<T>({{1, 2, X::empty},
-                          {3, 4, X::empty},
-                          {9, 10, X::empty},
-                          {11, 12, X::empty}});
-
-    test_ignore_empty<T>(
-        {{1, 2, "x"}, {3, 4, X::empty}, {9, 10, X::empty}, {11, 12, X::empty}});
-
-    test_ignore_empty<T>(
-        {{1, 2, X::empty}, {3, 4, X::empty}, {9, 10, X::empty}, {11, 12, "w"}});
-
-    test_ignore_empty<T>({{11, 12, X::empty}});
-
-    test_ignore_empty<T>({});
-}

test/test_parser1_5.cpp

@@ -0,0 +1,301 @@
+#include "test_parser1.hpp"
+
+TEST_CASE_TEMPLATE("test empty fields header", T, ParserOptionCombinations) {
+    constexpr auto buffer_mode = T::BufferMode::value;
+    using ErrorMode = typename T::ErrorMode;
+
+    unique_file_name f{"empty_fields_header"};
+
+    // Empty header
+    {
+        std::ofstream out{f.name};
+        out << "" << std::endl;
+        out << "1" << std::endl;
+    }
+
+    {
+        std::vector<std::string> expected_header = {""};
+        auto [p, _] = make_parser<buffer_mode, ErrorMode>(f.name);
+        CHECK_EQ_ARRAY(expected_header, p.header());
+        CHECK_EQ("", p.raw_header());
+        CHECK(p.valid());
+    }
+
+    // All empty header fields
+    {
+        std::ofstream out{f.name};
+        out << ",," << std::endl;
+        out << "1,2,3" << std::endl;
+    }
+
+    {
+        std::vector<std::string> expected_header = {"", "", ""};
+        auto [p, _] = make_parser<buffer_mode, ErrorMode>(f.name);
+        CHECK_EQ_ARRAY(expected_header, p.header());
+        CHECK_EQ(",,", p.raw_header());
+        CHECK(p.valid());
+
+        auto command1 = [&p = p] { std::ignore = p.field_exists("Int"); };
+        expect_error_on_command(p, command1);
+
+        auto command2 = [&p = p] { p.use_fields("Int"); };
+        expect_error_on_command(p, command2);
+    }
+
+    // One empty field
+    const std::vector<std::string> valid_fields = {"Int0", "Int1", ""};
+
+    using svec = std::vector<std::string>;
+    const std::vector<std::vector<std::string>> valid_field_combinations =
+        {svec{"Int0"},
+         svec{"Int1"},
+         svec{""},
+         svec{"", "Int0"},
+         svec{"Int0", "Int1"},
+         svec{"Int1", ""},
+         svec{"Int0", "", "Int1"},
+         svec{"", "Int1", "Int0"}};
+
+    // Last header field empty
+    {
+        std::ofstream out{f.name};
+        out << "Int0,Int1," << std::endl;
+        out << "1,2,3" << std::endl;
+    }
+
+    {
+        std::vector<std::string> expected_header = {"Int0", "Int1", ""};
+        auto [p, _] = make_parser<buffer_mode, ErrorMode>(f.name);
+        CHECK_EQ_ARRAY(expected_header, p.header());
+        CHECK_EQ("Int0,Int1,", p.raw_header());
+        CHECK(p.valid());
+
+        for (const auto& field : valid_fields) {
+            CHECK(p.field_exists(field));
+            CHECK(p.valid());
+        }
+
+        for (const auto& fields : valid_field_combinations) {
+            p.use_fields(fields);
+            CHECK(p.valid());
+        }
+    }
+
+    // First header field empty
+    {
+        std::ofstream out{f.name};
+        out << ",Int0,Int1" << std::endl;
+        out << "1,2,3" << std::endl;
+    }
+
+    {
+        std::vector<std::string> expected_header = {"", "Int0", "Int1"};
+        auto [p, _] = make_parser<buffer_mode, ErrorMode>(f.name);
+        CHECK_EQ_ARRAY(expected_header, p.header());
+        CHECK_EQ(",Int0,Int1", p.raw_header());
+        CHECK(p.valid());
+
+        for (const auto& field : valid_fields) {
+            CHECK(p.field_exists(field));
+            CHECK(p.valid());
+        }
+
+        for (const auto& fields : valid_field_combinations) {
+            p.use_fields(fields);
+            CHECK(p.valid());
+        }
+    }
+
+    // Middle header field empty
+    {
+        std::ofstream out{f.name};
+        out << "Int0,,Int1" << std::endl;
+        out << "1,2,3" << std::endl;
+    }
+
+    {
+        std::vector<std::string> expected_header = {"Int0", "", "Int1"};
+        auto [p, _] = make_parser<buffer_mode, ErrorMode>(f.name);
+        CHECK_EQ_ARRAY(expected_header, p.header());
+        CHECK_EQ("Int0,,Int1", p.raw_header());
+        CHECK(p.valid());
+
+        for (const auto& field : valid_fields) {
+            CHECK(p.field_exists(field));
+            CHECK(p.valid());
+        }
+
+        for (const auto& fields : valid_field_combinations) {
+            p.use_fields(fields);
+            CHECK(p.valid());
+        }
+    }
+}
+
+template <typename T, typename... Ts>
+void test_unterminated_quote_header() {
+    constexpr auto buffer_mode = T::BufferMode::value;
+    using ErrorMode = typename T::ErrorMode;
+
+    unique_file_name f{"unterminated_quote_header"};
+
+    {
+        std::ofstream out{f.name};
+        out << "\"Int" << std::endl;
+        out << "1" << std::endl;
+    }
+
+    {
+        auto [p, _] = make_parser<buffer_mode, ErrorMode, Ts...>(f.name);
+
+        auto command0 = [&p = p] { std::ignore = p.header(); };
+        expect_error_on_command(p, command0);
+        CHECK_EQ(p.raw_header(), "\"Int");
+
+        auto command1 = [&p = p] { std::ignore = p.field_exists("Int"); };
+        expect_error_on_command(p, command1);
+
+        auto command2 = [&p = p] { p.use_fields("Int"); };
+        expect_error_on_command(p, command2);
+    }
+}
+
+TEST_CASE_TEMPLATE("test unterminated quote header", T,
+                   ParserOptionCombinations) {
+    using quote = ss::quote<'"'>;
+    using escape = ss::escape<'\\'>;
+    test_unterminated_quote_header<T, quote>();
+    test_unterminated_quote_header<T, quote, ss::multiline>();
+    test_unterminated_quote_header<T, quote, escape>();
+    test_unterminated_quote_header<T, quote, escape, ss::multiline>();
+}
+
+template <typename T, typename... Ts>
+void test_unterminated_escape_header() {
+    constexpr auto buffer_mode = T::BufferMode::value;
+    using ErrorMode = typename T::ErrorMode;
+
+    unique_file_name f{"unterminated_escape_header"};
+
+    // Unterminated escape in header
+    {
+        std::ofstream out{f.name};
+        out << "Int\\" << std::endl;
+        out << "1" << std::endl;
+    }
+
+    {
+        auto [p, _] = make_parser<buffer_mode, ErrorMode, Ts...>(f.name);
+
+        auto command0 = [&p = p] { std::ignore = p.header(); };
+        expect_error_on_command(p, command0);
+        CHECK_EQ(p.raw_header(), "Int\\");
+
+        auto command1 = [&p = p] { std::ignore = p.field_exists("Int"); };
+        expect_error_on_command(p, command1);
+
+        auto command2 = [&p = p] { p.use_fields("Int"); };
+        expect_error_on_command(p, command2);
+    }
+}
+
+TEST_CASE_TEMPLATE("test unterminated escape header", T,
+                   ParserOptionCombinations) {
+    using quote = ss::quote<'"'>;
+    using escape = ss::escape<'\\'>;
+    test_unterminated_escape_header<T, escape>();
+    test_unterminated_escape_header<T, escape, ss::multiline>();
+    test_unterminated_escape_header<T, escape, quote>();
+    test_unterminated_escape_header<T, escape, quote, ss::multiline>();
+}
+
+template <typename T>
+void test_ignore_empty(const std::vector<X>& data) {
+    constexpr auto buffer_mode = T::BufferMode::value;
+    using ErrorMode = typename T::ErrorMode;
+
+    unique_file_name f{"ignore_empty"};
+    make_and_write(f.name, data);
+
+    std::vector<X> expected;
+    for (const auto& d : data) {
+        if (d.s != X::empty) {
+            expected.push_back(d);
+        }
+    }
+
+    {
+        auto [p, _] =
+            make_parser<buffer_mode, ErrorMode, ss::ignore_empty>(f.name, ",");
+
+        std::vector<X> i;
+        for (const auto& a : p.template iterate<X>()) {
+            i.push_back(a);
+        }
+
+        CHECK_EQ(i, expected);
+    }
+
+    {
+        auto [p, _] = make_parser<buffer_mode, ErrorMode>(f.name, ",");
+        std::vector<X> i;
+        size_t n = 0;
+        while (!p.eof()) {
+            try {
+                ++n;
+                const auto& a = p.template get_next<X>();
+                if (data.at(n - 1).s == X::empty) {
+                    CHECK_FALSE(p.valid());
+                    continue;
+                }
+                i.push_back(a);
+            } catch (...) {
+                CHECK_EQ(data.at(n - 1).s, X::empty);
+            }
+        }
+
+        CHECK_EQ(i, expected);
+    }
+}
+
+TEST_CASE_TEMPLATE("test various cases with empty lines", T,
+                   ParserOptionCombinations) {
+    test_ignore_empty<T>(
+        {{1, 2, "x"}, {3, 4, "y"}, {9, 10, "v"}, {11, 12, "w"}});
+
+    test_ignore_empty<T>(
+        {{1, 2, X::empty}, {3, 4, "y"}, {9, 10, "v"}, {11, 12, "w"}});
+
+    test_ignore_empty<T>(
+        {{1, 2, "x"}, {3, 4, "y"}, {9, 10, "v"}, {11, 12, X::empty}});
+
+    test_ignore_empty<T>(
+        {{1, 2, "x"}, {5, 6, X::empty}, {9, 10, "v"}, {11, 12, "w"}});
+
+    test_ignore_empty<T>(
+        {{1, 2, X::empty}, {5, 6, X::empty}, {9, 10, "v"}, {11, 12, "w"}});
+
+    test_ignore_empty<T>(
+        {{1, 2, X::empty}, {3, 4, "y"}, {9, 10, "v"}, {11, 12, X::empty}});
+
+    test_ignore_empty<T>(
+        {{1, 2, "x"}, {3, 4, "y"}, {9, 10, X::empty}, {11, 12, X::empty}});
+
+    test_ignore_empty<T>(
+        {{1, 2, X::empty}, {3, 4, "y"}, {9, 10, X::empty}, {11, 12, X::empty}});
+
+    test_ignore_empty<T>({{1, 2, X::empty},
+                          {3, 4, X::empty},
+                          {9, 10, X::empty},
+                          {11, 12, X::empty}});
+
+    test_ignore_empty<T>(
+        {{1, 2, "x"}, {3, 4, X::empty}, {9, 10, X::empty}, {11, 12, X::empty}});
+
+    test_ignore_empty<T>(
+        {{1, 2, X::empty}, {3, 4, X::empty}, {9, 10, X::empty}, {11, 12, "w"}});
+
+    test_ignore_empty<T>({{11, 12, X::empty}});
+
+    test_ignore_empty<T>({});
+}